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Practical effects of finiteness

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The speed of light is of relevance to communications: the one-way and round-trip delay time are greater than zero. This applies from small to astronomical scales. On the other hand, some techniques depend on the finite speed of light, for example in distance measurements. Small scales In supercomputers, the speed of light imposes a limit on how quickly data can be sent between processors. If a processor operates at 1   gigahertz, a signal can travel only a maximum of about 30 centimetres (1 ft) in a single cycle. Processors must therefore be placed close to each other to minimize communication latencies; this can cause difficulty with cooling. If clock frequencies continue to increase, the speed of light will eventually become a limiting factor for the internal design of single chips. Large distances on Earth Given that the equatorial circumference of the Earth is about 40 075  km and that c is about 300 000  km/s , the theoretical shortest time for a piece of information to travel ...
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Numerical value, notation, and units

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The speed of light in vacuum is usually denoted by a lowercase c , for "constant" or the Latin celeritas (meaning "swiftness, celerity"). In 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch had used c for a different constant that was later shown to equal √ 2 times the speed of light in vacuum. Historically, the symbol V was used as an alternative symbol for the speed of light, introduced by James Clerk Maxwell in 1865. In 1894, Paul Drude redefined c with its modern meaning. Einstein used V in his original German-language papers on special relativity in 1905, but in 1907 he switched to c , which by then had become the standard symbol for the speed of light. Sometimes c is used for the speed of waves in any material medium, and c 0 for the speed of light in vacuum. This subscripted notation, which is endorsed in official SI literature, has the same form as other related constants: namely, μ 0 for the vacuum permeability or magnetic constant, ε 0 for the v...
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Speed of light

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The speed of light in vacuum, commonly denoted c , is a universal physical constant important in many areas of physics. Its exact value is defined as 299 792 458  metres per second (approximately 300 000  km/s, or 186 000  mi/s).Note It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of ​ 1⁄ 299 792 458 second.Note According to special relativity, c is the upper limit for the speed at which conventional matter, energy or any information can travel through coordinate space. Though this speed is most commonly associated with light, it is also the speed at which all massless particles and field perturbations travel in vacuum, including electromagnetic radiation (of which light is a small range in the frequency spectrum) and gravitational waves. Such particles and waves travel at c regardless of the motion of the source or the inertial reference frame of the observer. Particles with nonze...
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